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1.
针对高温含水条件下非氧化物材料经常面临的性能失效问题,以六方BN粉体(平均粒度为1.2μm)为研究对象,利用高温热重分析、X射线衍射以及扫描电镜等手段,考察了BN粉体在不同温度(1273-1373K)含水条件下f水和空气的体积比为3:7)的反应行为,并与其在干燥空气下的反应行为进行对比.BN粉体在含水条件下的反应有如下特点:在反应初期,试样质量增加率快速增加;在反应后期,试样质量增加率变缓.结合热力学分析探讨了BN材料在高温含水条件下的反应机理:质量快速增加阶段主要发生BN与O2之间的氧化反应,试样质量增加率变缓阶段主要是由于氧化产物B2O3与H2O反应生成了挥发性产物.随着温度的升高,两反应阶段试样的质量增加率均有所提高.利用周模型对BN材料在高温含水条件下的反应动力学进行了较为精确且定量的拟合,结果与实验数据吻合良好. 相似文献
2.
提出了高炉铁水双辊连铸薄带十高温气固反应脱碳,生产钢带的全新工艺流程.实验以高碳铁碳合金板带为研究对象,在Ar-H2-H2O气氛下可控气氛管式炉内,利用高温气固反应脱碳机制,探索铁碳合金固态下脱碳而铁基不氧化的可行性,确定可控气氛下脱碳的温度和气氛条件范围.实验结果表明:气氛条件对铁的氧化有显著影响,当水浴温度不大于60℃或气体流量不大于300 mL/min时,脱碳后基体中不存在铁的氧化物;当水浴温度达到70℃或气体流量达到450mL/min时,脱碳后基体中出现铁的氧化物,此时由于铁氧化的出现降低了脱碳效果. 相似文献
3.
本文对含无毒性非氧化物加入剂AlN,AlN+ZrN,ZrN的Si_3N_4陶瓷材料的高温性能作了比较细致的研究,并与含MgO.Al_2O_3,MgO,BeSiN_2的陶瓷材料作了对比。研究表明,采用复合加入剂AlN+ZrN,避免了BeSiN_2有毒及其材料常温力学性能不佳的问题,在很大程度上提高了Si_3N_4材料的高温性能。其在1400℃下的氧化速率常数较之以MgO.Al_2O_3为加入剂的Si_3N_4材料低两个数量级,1400℃的抗弯强度与室温强度的比值由41.5%提高到71%,同时抗热震性相当好(△Tc≥900℃),从而为在高温度、高应力条件下使用Si_3N_4瓷陶材料提供了一条有效的途径。 相似文献
4.
采用SRV-Ⅳ高精度微动磨损试验机研究核电材料Inconel600合金的高温微动磨损行为和机制.温度升高有利于黏着区的形成,抑制微滑区的产生,促使摩擦系数和磨损量逐渐减小.摩擦氧化主要发生在环状滑动区,中心黏着区相对很少.高温下氧元素分布较室温下的更加聚集.中心黏着区表面氧含量较低,表层大量存在Ni、Cr和Fe的单质.磨痕表面氧化物由NiO、Cr2O3和Fe3O4组成.室温和高温条件下磨痕表面中心黏着区和环状滑动区交界处产生了微裂纹,高温下裂纹萌生在微滑区,与室温下相比,高温下裂纹萌生的数量更少,长度更短. 相似文献
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(Ce-Zr)mA1-mO2复合氧化物的制备及其表征 总被引:2,自引:2,他引:0
以碳酸铵为沉淀剂,采用共沉淀法制备铈锆、铈锆镧、铈锆镨复合氧化物,通过X射线衍射(XRD)、BET法和程序升温还原(TPR)等手段对复合氧化物进行了表征,研究了高温焙烧条件下不同铈锆摩尔比和掺杂镧镨对复合氧化物的结构和性能的影响,并初步分析了掺杂La和Pr的作用机理.结果表明, Ce0.76Zr0.24O2在高温焙烧后仍然保持着立方相的固溶体结构,衍射峰没有发生分裂,有着比较好的高温热稳定性;掺杂La和Pr以后均能在一定程度上提高氧化物的热稳定性. 相似文献
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殷声 《粉末冶金材料科学与工程》1997,(3)
传统供热燃烧是利用燃料和氧化剂的反应获得热能。自蔓延高温合成(SHS)则是利用燃料和氧化剂的放热反应制备有用材料。根据SHS的燃料和氧化剂的种类,SHS的反应体系可分为两类:元素间的直接合成;以化合物为反应物的合成。前者,在绝大多数情况下,金属元素是燃料,非金属元素是氧化剂,属无氧燃烧。后者,燃料是金属或低价氧化物,氧化剂是氧化物、过氧化物、气体氧或非金属。文中讨论了燃烧中的化学反应、反应机制和产物。 相似文献
9.
利用热力学计算,分析了几种氧化物涂层Y2O3、ZrO2、Al2O3、MgO、CaO、Ce2O3和BeO等在高温下与新型铌硅化物基超高温合金中的几种主要元素Nb、Si、Ti和Hf之间反应的可能性,得到了这些反应的△G^-与温度T的关系图。通过比较这几种氧化物对合金熔体在高温下的化学稳定性,发现Y2O3和BeO对这些合金元素的化学稳定性较好,且Y2O3为熔炼铌硅化物基超高温合金用石墨坩埚的理想涂层材料。 相似文献
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铁矿石烧结烟气中含有较高浓度的CO(体积分数0.5%~2%),因此对其进行CO脱除意义重大。为了探究不同类型催化剂的催化效果,采用浸渍法制备了Pt涂层蜂窝金属催化剂和铁铈氧化物催化剂,并通过X射线荧光光谱分析(XRF)对其组分含量进行了分析。二者在模拟烧结烟气中进行CO脱除性能的对比实验,活性测试表明,不同CO初始体积分数、烟气温度以及水汽含量对CO催化氧化的脱除效率影响较大。当模拟烟气中不含水汽的时候,二者在180 ℃及更高温度下对CO的脱除效率均能达到60%以上。反应温度为180 ℃,水汽体积分数为11.7%时,Pt负载型催化剂中的CO转化率为63.9%,而该条件下Ce改性Fe2O3催化剂的CO转化率仅为34.9%。当温度在180~300 ℃范围内,Pt负载型催化剂具有较好的抗水性,且继续升高温度,水汽体积分数增加对催化剂效率的负面影响更显著。如水汽体积分数从0增加到27.1%时,与180 ℃时的催化效率相比,Pt负载型催化剂在240 ℃时的催化效率由73.9%降至62.3%,降幅远远增大。另外,对这两种催化剂进行了抗硫性测试。当水汽体积分数为0时,Ce改性Fe2O3催化剂抗硫性更佳,但当SO2和水汽同时存在的情况下,Pt负载型催化剂具有更好的抗硫性。因此,在实际烧结中建议采取高效的脱硫措施并布置脱水层以减少其对于催化剂的负面影响。 相似文献
12.
Thermodynamic conditions of reactions between high-carbon ferromanganese powders and gas decarbonizers like O2, CO2 and water vapor were studied by thermodynamic calculation. In O2, CO2 and water vapor atmosphere, high-carbon ferromanganese powders were decarburized in a fluidized bed. When the temperature is respectively higher than 273, 1226 and 1312 K, the gas-solid decarburization reaction will occur between ferromanganese carbide on the surface of the high-carbon ferromanganese powders and different gas decarbonizers. Since metal manganese is easy to be oxidized by O2, CO2 or water vapor, the decarburization reaction will transfer into a solid-solid phase reaction of ferromanganese carbide and ferromanganese oxide, promoting external diffusion of carbon to achieve a further decarburization of high-carbon ferromanganese powders. 相似文献
13.
Fracture mechanics and surface chemistry studies of fatigue crack growth in an aluminum alloy 总被引:3,自引:0,他引:3
R. P. Wei P. S. Pao R. G. Hart T. W. Weir G. W. Simmons 《Metallurgical and Materials Transactions A》1980,11(1):151-158
Fracture mechanics and surface chemistry studies were carried out to develop further understanding of the influence of water
vapor on fatigue crack growth in aluminum alloys. The room temperature fatigue crack growth response was determined for 2219-T851
aluminum alloy exposed to water vapor at pressures from 1 to 30 Pa over a range of stress intensity factors (K). Data were also obtained in vacuum (at < 0.50 μPa), and dehumidified argon. The test results showed that, at a frequency
of 5 Hz, the rate of crack growth is essentially unaffected by water vapor until a threshold pressure is reached. Above this
threshold, the rates increased, reaching a maximum within one order of magnitude increase in vapor pressure. This maximum
crack growth rate is equal to that obtained in air (40 to 60 pct relative humidity), distilled water and 3.5 pct NaCl solution
on the same material. Parallel studies of the reactions of water vapor with fresh alloy surfaces (produced either byin situ impact fracture or by ion etching) were made by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS).
The extent of surface reaction was monitored by changes in the oxygen AES and XPS signals. Correlation between the fatigue
crack growth response and the surface reaction kinetics has been made, and is consistent with a transport-limited model for
crack growth. The results also suggest that enhancement of fatigue crack growth by water vapor in the aluminum alloys occurs
through a “hydrogen embrittle ment” mechanism. 相似文献
14.
设计建立了一套以水为工质的分离式热管系统实验台,系统冷凝端采用水冷套管式换热器。在此实验台基础上研究了不抽真空,有大量不凝性气体空气存在于分离式热管的蒸汽凝结放热问题。测定了不同的蒸汽入口温度、循环蒸汽流量、冷却水进口温度及流量四种情况下混合气体在圆管内凝结放热的情况,分析了这些参数对换热过程的影响。 相似文献
15.
JT Wang GK Shiu T Ong-Chen CT Viswanathan JP Skelly 《Canadian Metallurgical Quarterly》1993,82(10):1002-1005
The rate and extent of dissolution of various approved marketed carbamazepine (CBZ) tablets exposed to 33, 52, 75, and 97% relative humidities at both room temperature and 40 degrees C, and saturated water vapor at room temperature were compared to fresh unstressed tablets. The dissolution data indicate that exposure of CBZ tablets to high humidity and temperature can have a profound effect on tablet disintegration and dissolution. The dissolution rates of some batches of CBZ products exposed to 97% humidity at 40 degrees C or saturated water vapor at room temperature were drastically reduced in only 6-7 days. 相似文献
16.
Coordinated fracture mechanics and surface chemistry experiments were carried out to develop further understanding of environment
enhanced subcritical crack growth in high strength steels. The kinetics of crack growth were determined for an AISI 4340 steel
(tempered at 204°C) in hydrogen and in water, and the kinetics for the reactions of water with the same steel were also determined.
A regime of rate limited (Stage II) crack growth was observed in each of the environments. Stage II crack growth was found
to be thermally activated, with an apparent activation energy of 14.7 ±2.9 kJ/mole for crack growth in hydrogen, and 33.5
± 5.0 kJ/mole in water. Fractographic evidence indicated that the fracture path through the microstructure was the same for
these environments, and suggested hydrogen to be the embrittling species for environment enhanced crack growth in hydrogen
and in water/water vapor. A slow step in the surface reaction of water vapor with steel was identified, and exhibited an activation
energy of 36 ± 14 kJ/ mole. This reaction step was identified to be that for the nucleation and growth of oxide. The hydrogen
responsible for embrittlement was presumed to be produced during this reaction. On the basis of a comparison of the activation
energies, in conjunction with other supporting data, this slow step in the water/metal surface reaction was unambiguously
identified as the rate controlling process for crack growth in water/water vapor. The inhibiting effect of oxygen and the
influence of water vapor pressure on environment enhanced subcritical crack growth were considered. The influence of segregation
of alloying and residual impurity elements on crack growth was also considered. 相似文献
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18.
P. Hayes 《Metallurgical and Materials Transactions B》1979,10(4):489-496
The effects of adsorbed impurities on the kinetics of reactions on metal surfaces are discussed, in particular the reactions
of water vapor and carbon dioxide with iron surfaces are analyzed. The critical oxygen potentials for the onset of ‘poisoning’
of the reactions appear to correspond with the onset of facetting of iron and the formation of surface phases on the iron.
The maximum chemical reaction rate constants for the reactions of water vapor and of carbon dioxide on iron surfaces at a
given temperature are shown to correspond closely to the chemical reaction rate constants determined from the reduction of
iron oxides in their respective systems. The phenomena observed on the reaction of gases with iron and iron oxide surfaces
are reported in other metal systems thus the analysis used for the present reactions appears to be applicable to other systems
involving metal/gas reactions. 相似文献
19.
摘要:日本福岛核电站泄漏事故暴露了锆合金易与水蒸气反应造成爆炸的缺陷,又将人们的视线拉回了各项性能较为均衡的FeCrAl合金。FeCrAl合金较锆合金具有更好的耐腐蚀性能,更能满足核反应堆高温水蒸气环境下的工作条件。为进一步保障核反应堆安全性,各国学者对FeCrAl合金的性能进行了大量研究。基于此,综述了FeCrAl合金腐蚀机制及其在高温蒸汽和高温水环境中的腐蚀行为;探讨了合金元素(稀土、Ti、Zr、Nb和Mo)、变形和热处理对合金力学性能的影响;总结了FeCrAl合金辐照性能和焊接性能的研究进展。最后指出了核级FeCrAl合金在研究中存在的不足及未来重点发展方向,为今后其他学者在该领域的研究提供参考。 相似文献